The present invention relates to a master cylinder for operating a brake device, a clutch device or the like in an automobile, and more particularly to an improvement of a master cylinder in which a bearing housing is coupled to a rear end of a cylinder hole of a cylinder body through a step portion expanding outwardly in a radial direction, a bearing is fitted into the bearing housing so that the bearing slidably supports a piston rod projecting from a rear end surface of a piston in the cylinder hole, a stopper ring is engaged on the side of an entrance of the bearing housing, the bearing is held by the step portion and the stopper ring, a seal member is slidably engaged on an outer circumferential surface of the piston rod, and an inner circumferential seal groove is formed on an inner circumferential surface of the bearing for fitting the seal member thereinto.
Such a conventional master cylinder is disclosed in e.g., Examined Japanese Utility Model Publication No. Hei. 1-43344. With the conventional master cylinder, a bearing is restrained from moving in an axial direction in such a manner that a circlip serving as a stopper ring is opposite to a rear end surface of the integrated bearing. However, a clearance is unavoidably generated by processing between opposite surfaces of the bearing and circlip. Therefore, the bearing generates a chatter noise due to the clearance. Further, since an inner circumferential seal groove, which is formed on an inner circumferential surface of the bearing, has a U-shape in longitudinal section along a center axis of a cylinder body, a seal member must be seriously deformed for being fitted into the inner circumferential seal groove, thereby to be in danger of damaging the seal member.